linux-kernel - Re: [PATCH 1/1] pstore/ram: Ensure stable pmsg address with per-CPU ftrace buffers

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Date:   Tue, 11 Oct 2022 12:38:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     pso@...omium.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        Dmitry Torokhov <dtor@...omium.org>,
        Paramjit Oberoi <psoberoi@...gle.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 1/1] pstore/ram: Ensure stable pmsg address with per-CPU
 ftrace buffers

On Tue, Oct 11, 2022 at 11:36:31AM -0700, pso@...omium.org wrote:
> From: Paramjit Oberoi <psoberoi@...gle.com>
> 
> When allocating ftrace pstore zones, there may be space left over at the
> end of the region. The paddr pointer needs to be advanced to account for
> this so that the next region (pmsg) ends up at the correct location.
> 
> Signed-off-by: Paramjit Oberoi <pso@...omium.org>
> Reviewed-by: Dmitry Torokhov <dtor@...omium.org>
> Signed-off-by: Paramjit Oberoi <psoberoi@...gle.com>

Hm, interesting point. Since only ftrace is dynamically sized in this
fashion, how about just moving the pmsg allocation before ftrace, and
adding a comment that for now ftrace should be allocated last?

i.e. something like:

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 650f89c8ae36..9e11d3e7dffe 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -788,6 +788,11 @@ static int ramoops_probe(struct platform_device *pdev)
        if (err)
                goto fail_init;
 
+       err = ramoops_init_prz("pmsg", dev, cxt, &cxt->mprz, &paddr,
+                               cxt->pmsg_size, 0);
+       if (err)
+               goto fail_init;
+
        cxt->max_ftrace_cnt = (cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)
                                ? nr_cpu_ids
                                : 1;
@@ -799,11 +804,6 @@ static int ramoops_probe(struct platform_device *pdev)
        if (err)
                goto fail_init;
 
-       err = ramoops_init_prz("pmsg", dev, cxt, &cxt->mprz, &paddr,
-                               cxt->pmsg_size, 0);
-       if (err)
-               goto fail_init;
-
        cxt->pstore.data = cxt;
        /*
         * Prepare frontend flags based on which areas are initialized.

(Note that this won't apply to the current tree, where I've started some
other refactoring.)

-- 
Kees Cook